The publication, "Evaluating Polyimides as Lightguide Materials," by R. Reuter et al., Applied Optics, Vol. 27, No. 21, Nov. 1, 1988, pp. 4565-4570, describes the use of a number of different polymers as media for transmitting lightwaves. Various polymer materials such as polymethyl methacrylate and various polyimides have been proposed as materials from which lightguide or optical waveguide patterns can be made on a flat substrate. Such films may be only a few microns in thickness and can be used to transmit light to optoelectronic devices on a substrate much the way printed circuits transmit electrical current on a printed wiring board. Effective transmission requires that the optical waveguide material have a relatively low attenuation or loss with respect to the light beam transmitted and that it have a higher optical index of refraction than the surrounding media. The materials mentioned in the paper have a sufficiently high index of refraction and a sufficiently low loss, at least at certain optical frequencies, to be useful as practical media for optical waveguide purposes.
The article points out that a major disadvantage of polymethyl methacrylate is its poor thermal and environmental stability. Disadvantages of polyimides include their high cure temperature, typically above three hundred degrees Centigrade, which could be damaging to certain substrates such as printed wiring boards made of commonly used resin materials, and their relatively high cost.
There is therefore a continued long-felt need for polymer waveguides that can transmit light with low loss and high efficiency, that have good thermal and environmental stability, can be made without subjecting them to inordinately high cure temperatures, are of low cost, and are amenable to mass production.